A meter has a scale of possible values to which it is responsive. This scale is established by the construction of the meter. Generally, for increased accuracy, the total scale of response is divided into ranges to which, by manipulation of switching mechanisms associated with the meter, the full scale deflection of the meter is limited at any one instance. For example, the meter may have a scale of 0-10, and ranges of 0-1, 1-2, 2-3, etc. The range to which the meter is responsive is determined by the manipulation of the switching mechanisms of the meter and is usually done manually.
Situations are frequently encountered where it is necessary to measure with the meter some experimental parameter over long periods of time. If the parameter changes by a few orders of magnitude during that time, but it is still desired to analyze relatively small changes in the value of the parameter, then it is necessary to provide some means for switching between the scales of the meter to encompass all possible values of the parameter. With a meter requiring manual switching between scales, continuous observation over the time period involved is necessary. Avoidance of continuous observation may be achieved by choosing a full scale deflection which covers the entire expected change. In this case small effects will probably be lost due to the inability to finely select a full scale deflection. Another method would be to use a recorder with a logarithmic response. Unfortunately, this also may compress the effects at larger values. Ideally one should be able to have an expanded scale of response with multiple ranges with turning of a switch. A full scale deflection is added or subtracted each time the instrument goes off scale until the scale encompassing the unknown is reached.
It is therefore an object of this invention to provide a means for automatically selecting from a plurality of ranges of a scale of values the range to which a meter will be responsive.